CN217508580U

CN217508580U - Low-power-consumption LDO constant-current starting circuit in switching power supply

Info

Publication number: CN217508580U
Application number: CN202221410869.XU
Authority: CN
Inventors: 习美泉; 杨梅英; 方勇
Original assignee: Jiangsu Zhaoneng Electronic Co ltd
Current assignee: Jiangsu Zhaoneng Electronic Co ltd
Priority date: 2022-06-07
Filing date: 2022-06-07
Publication date: 2022-09-27
Anticipated expiration: 2032-06-07

Abstract

The utility model provides a low-power consumption LDO constant current starting circuit among switching power supply, this circuit contains input voltage source, primary side power line, coupling isolation transformer, secondary side rectifier circuit, PWM control chip, auxiliary power source Vcc generation circuit, LDO constant current starting circuit between former secondary side, the output of auxiliary power source Vcc generation circuit connects the power supply port of PWM control chip, the input of LDO constant current starting circuit is connected input voltage source, the output connects the power supply port of PWM control chip; the utility model provides a pair of this kind of switching power supply starting circuit utilizes the N type MOS pipe of depletion type for starting circuit is controllable at switching power supply start-up's in-process electric current, and the electric current is little, and the heat loss is little, makes the MOS pipe lectotype of LDO circuit more convenient, can realize, and does not have extra increase part, and the circuit is simple, and the commonality is strong, easily realizes.

Description

Low-power LDO constant current starting circuit in switching power supply

Technical Field

The utility model relates to a switching power supply field, concretely relates to low-power consumption LDO constant current starting circuit among switching power supply.

Background

In the starting process of the switching power supply, the system is not completely started, the output voltage is not established, and an auxiliary power supply Vcc generation circuit cannot provide the power supply voltage required by the PWM control chip, so that an LDO starting circuit is needed, the input end of the LDO starting circuit is connected with the input voltage to output the stable power supply voltage required by the PWM control chip, usually about 12V, and after the switching power supply system is completely established, the power supply voltage of the PWM control chip is generated by the auxiliary power supply Vcc generation circuit, low-voltage power supply is realized, and the power consumption generated by a power supply line is reduced; in the starting circuit, the input of a switch tube is connected with an input voltage source, the output of low voltage of about 12V is not difficult, and the problem of heat can be solved, but with the requirement of the current application market, particularly the development of the EV power supply market, the switching power supply with high-voltage input is more and more required, for example, in figure 1, a circuit 10 is an LDO starting circuit of the prior art, the switch tube Q2 is an N-type enhanced MOS tube, the drain electrode of the N-type enhanced MOS tube is connected with the input voltage, the source electrode provides the power supply voltage of a PWM control chip, the voltage difference between the drain electrode and the source electrode is very large, and the passing current is large and uncontrollable, so the heat loss of the switch tube Q2 in the starting process of the switching power supply is large, and in order to solve the problem of heat, a high-power MOS tube is selected, thereby bringing pressure to the cost and the space, even if the cost and the space are not considered, a proper MOS tube is sometimes difficult to find, and the type selection is difficult.

In order to solve the problem, the utility model provides a low-power consumption LDO constant current starting circuit among switching power supply.

SUMMERY OF THE UTILITY MODEL

The utility model provides a technical problem provide a low-power consumption LDO constant current starting line.

The utility model provides a technical scheme that above-mentioned technical problem adopted is:

a low-power LDO constant current starting circuit in a switching power supply comprises an input voltage source, an input filter circuit, a primary power circuit, an isolation transformer coupled between an original side and a secondary side, a secondary side rectifying circuit, an output filter circuit, a PWM control chip, an auxiliary power supply Vcc generating circuit and an LDO constant current starting circuit, wherein the output of the auxiliary power supply Vcc generating circuit is connected with a power supply port of the PWM control chip; the input end of the LDO constant current starting circuit is connected with an input voltage source, and the output end of the LDO constant current starting circuit is connected with a power supply port of the PWM control chip.

Furthermore, the LDO constant current starting circuit includes a first MOS transistor, a first resistor, a first capacitor, a second capacitor, and a first voltage regulator, a drain of the first MOS transistor and one end of the first capacitor are connected to a positive terminal of the input voltage source, a source of the first MOS transistor is connected to one end of the first resistor, a gate of the first MOS transistor is connected to one end of the second capacitor, a cathode of the first voltage regulator, the other end of the first resistor, and the power supply port of the PWM control chip, and the other end of the first capacitor, the other end of the second capacitor, and an anode of the first voltage regulator are connected to a negative terminal of the input voltage source.

Further, the first MOS transistor is a depletion type N-type MOSFET.

Furthermore, the auxiliary power supply Vcc generation circuit comprises an auxiliary winding and a first diode, wherein one end of the auxiliary winding is connected with the ground of the primary side of the switching power supply, the other end of the auxiliary winding is connected with the anode of the first diode, and the cathode of the first diode is connected with the power supply port of the PWM control chip.

Further, the auxiliary winding is coupled to the isolation transformer and is in phase with the secondary winding of the isolation transformer.

Further, the PWM control chip outputs a PWM control signal to a power switch tube of the primary power circuit directly or indirectly through a driving circuit.

Furthermore, the input voltage source is connected with the input filter circuit and then connected with the primary power circuit, the output of the primary power circuit is connected with the primary winding of the isolation transformer, and the secondary winding of the isolation transformer is connected with the secondary rectifier circuit and then connected with the output filter circuit.

The utility model discloses for the technological effect that prior art gained does:

the utility model provides a pair of this kind of switching power supply LDO starting line utilizes a depletion type's N type MOS pipe for starting line is controllable at switching power supply machine-starting's in-process electric current, and the electric current is little, and the heat loss is little, and the MOS pipe type selection in the LDO circuit is convenient, and does not have extra increase part, and the circuit is simple, and the commonality is strong, easily realizes.

Drawings

Fig. 1 is a circuit diagram of a prior art LDO start-up circuit in a switching power supply.

Fig. 2 is an embodiment of the low power consumption LDO constant current start circuit provided by the present invention.

Detailed Description

The circuit of the present invention is provided in the following embodiments with reference to the accompanying drawings to explain the technical solutions of the present invention in detail.

As shown in fig. 2, an input voltage source is connected with an input filter circuit and then connected with a primary power circuit, the output of the primary power circuit is connected with a primary winding of an isolation transformer, a secondary winding of the isolation transformer is connected with an output filter circuit after being connected with a secondary rectifier circuit, and the output of an auxiliary power supply Vcc generation circuit is connected with a power supply port of a PWM control chip; the input end of the LDO constant current starting circuit is connected with an input voltage source, and the output end of the LDO constant current starting circuit is connected with a power supply port of the PWM control chip.

The line 20 is an LDO constant current start-up line, and includes a first MOS transistor Q1, a first resistor R1, a first capacitor C1, a second capacitor C2, and a first voltage regulator ZD1, the first MOS transistor Q1 is a depletion N-type MOSFET, the drain of the first MOS transistor Q1 is connected to the positive terminal of the input voltage source together with one end of C1, the source of the first MOS transistor Q1 is connected to one end of the R1, the gate of the first MOS transistor Q1 is connected to one end of the C2, the cathode of the ZD1, the other end of the R1, and the power supply port Vdd of the PWM control chip, and the other end of the C1, the other end of the C2, and the anode of the ZD1 are connected to the negative terminal of the input voltage source.

The circuit 30 is a simple circuit diagram of an auxiliary power supply Vcc generation circuit, and comprises an auxiliary winding and a first diode CR1, wherein one end of the first diode CR1 is connected with the ground of the primary side of the switching power supply, the other end of the first diode CR1 is connected with the anode of the CR1, and the cathode of the CR1 is connected with the power supply port Vdd of the PWM control chip; the auxiliary winding is coupled to the isolation transformer and is in phase with the secondary winding of the isolation transformer.

The PWM control chip outputs a PWM control signal to a power switch tube of a primary power circuit directly or indirectly through a driving circuit; the switching power supply topology architecture is not limited to the flyback architecture, and can be a forward or bridge architecture.

The working principle of the low-power LDO constant current starting circuit is as follows:

during the startup process of the switching power supply, the output voltage Vo is not established, the voltage coupled by an auxiliary winding in an auxiliary power supply Vcc generation circuit is not enough to maintain the work of a PWM control chip, therefore, in the startup process of the switching power supply, the power supply of the PWM control chip is provided by the LDO starting circuit, as shown in fig. 2, ZD1 is a regulator of about 12V, Q1 is a depletion N-type MOS transistor, the drain-source (DS) electrode current, can be regulated by changing the resistance of R1, the resistance of R1 is large, the current passing through the drain-source (DS) pole of Q1 is small, the working temperature of Q1 is low, the loss generated by a starting circuit is small, and after R1 is determined, under the determined input voltage, the current flowing through R1 is constant, so that the low-power-consumption constant-current starting is really realized, therefore, under the condition of outputting the same power, the Q1 can select the MOS tube type with small package and low power, and the cost and the power density are ensured.

Although specific implementations of the invention have been described above, it will be appreciated by those skilled in the art that these are merely examples and that many variations or modifications may be made to these implementations without departing from the principles and spirit of the invention. The scope of protection of the invention is therefore defined by the appended claims.

Claims

1. A low-power LDO constant current starting circuit in a switching power supply is characterized by comprising an input voltage source, an input filter circuit, a primary power circuit, an isolation transformer coupled between an original side and a secondary side, a secondary side rectifying circuit, an output filter circuit, a PWM control chip, an auxiliary power supply Vcc generating circuit and an LDO constant current starting circuit, wherein the output of the auxiliary power supply Vcc generating circuit is connected with a power supply port of the PWM control chip; the input end of the LDO constant current starting circuit is connected with an input voltage source, and the output end of the LDO constant current starting circuit is connected with a power supply port of the PWM control chip.

2. The LDO constant current starting circuit with low power consumption in a switching power supply as claimed in claim 1, wherein the LDO constant current starting circuit comprises a first MOS transistor, a first resistor, a first capacitor, a second capacitor, and a first voltage regulator, a drain electrode of the first MOS transistor and one end of the first capacitor are connected to a positive terminal of an input voltage source, a source electrode of the first MOS transistor is connected to one end of the first resistor, a gate electrode of the first MOS transistor is connected to one end of the second capacitor, a cathode electrode of the first voltage regulator, the other end of the first resistor and a power supply port of the PWM control chip, and the other end of the first capacitor, the other end of the second capacitor and an anode electrode of the first voltage regulator are connected to a negative terminal of the input voltage source.

3. The LDO constant current start-up circuit with low power consumption in switching power supply as claimed in claim 2, wherein said first MOS transistor is a depletion type N-type MOSFET.

4. The LDO constant current start circuit with low power consumption of claim 1, wherein the auxiliary power supply Vcc generation circuit comprises an auxiliary winding, a first diode having one end connected to the ground of the primary side of the switching power supply and the other end connected to the anode of the first diode, and the cathode of the first diode connected to the power supply port of the PWM control chip.

5. The LDO constant current start circuit with low power consumption of claim 4, wherein the auxiliary winding is coupled to the isolation transformer and is in phase with a secondary winding of the isolation transformer.

6. The LDO constant current startup circuit with low power consumption in a switching power supply as claimed in claim 1, wherein the PWM control chip outputs the PWM control signal to the power switch tube of the primary power line directly or indirectly through the driving circuit.

7. The LDO constant current start circuit with low power consumption in a switching power supply as claimed in claim 1, wherein the input voltage source is connected with the input filter circuit and then connected with the primary power circuit, the output of the primary power circuit is connected with the primary winding of the isolation transformer, and the secondary winding of the isolation transformer is connected with the secondary rectifier circuit and then connected with the output filter circuit.